Typically, as power systems for an aircraft, three kinds of systems, which are a hydraulic system, a bleed air system, and an electric system, are mounted in the aircraft. The hydraulic system is used for the operations of landing gears, control surfaces, etc. The bleed air system is used for the operations of air conditioning devices, pressure application devices, de-icing devices, and others, which are equipped inside the aircraft. The electric system is used for the operations of electric devices and electronic devices. In recent years, there has been a trend that at least a portion of the hydraulic system and a portion of the bleed air system are replaced by the electric system with a higher efficiency. For example, as actuators (including an actuator for controlling the control surface) included in the aircraft, electric (electrically powered) actuators have been widely used, instead of conventional hydraulic (hydraulically powered) actuators. The aircraft in which the hydraulic system, the bleed air system, and other systems are replaced as much as possible by the electric system, is typically named more electric aircraft (MEA).
It is known that with a progress of the MEA, an amount of a change (fluctuation) in a voltage or frequency in the electric system increases, and the electric system becomes unstable. For example, in the case of the electric actuator, regenerative power with a great magnitude is generated (electric power with a great magnitude is returned) from a driving motor, and thereby a voltage in the electric system significantly rises temporarily (for a certain time). In addition, the regenerative power is sent to a generator mounted in an engine, and thereby an engine gear box might be adversely affected due to backlash. Or, if power loads (devices mounted in the aircraft and supplied with electric power from the electric system) supplied with the electric power from the electric system, increase temporarily, a significant voltage decrease (drop) may occur.
It is known that in the electric system in which the MEA has progressed, various configurations are used to deal with the above-described voltage increase or voltage decrease (drop). For example, Patent Literature 1 discloses that a bidirectional electric accumulator is provided in an electric system to absorb the regenerative power (excess electric power) from an actuator. In another example, Patent Literature 2 discloses that regenerative power from an actuator is released to a power sink and absorbed. As examples of the power sink, a plurality of auxiliary loads or generators are described in Patent Literature 2.